Brian Snyder/REUTERSHeavily armed police offers arrive on the scene of the manhunt.

Brian Snyder/REUTERSAn officer aims his gun at a suspect.

Brian Snyder/REUTERSA man is ordered to the ground by police. It is unclear whether he was later released.

REUTERS/Lucas JacksonLaw enforcement officials stage in a parking lot during a search for the two men suspected of setting off two explosions during the Boston Marathon in Watertown, Massachusetts, April 19, 2013.

Lucas Jackson/REUTERsA law enforcement official checks his rifle during the police search.

Hospital officials who treated Suspect 1 suggested he may have been wearing an explosive device, although they would not confirm this.